Accelerated weathering test method

ABSTRACT

The present invention provides an accelerated weathering test method, which gives the results having a high correlation with the results of natural exposure and can significantly reduce a test duration. An accelerated weathering test method for a coating film with a remote plasma apparatus, wherein it is possible to bring the interior of the remote plasma apparatus into a reduced pressure and introduce gas, for example oxygen gas, into the apparatus.

TECHNICAL FIELD

The present invention relates to an accelerated weathering test method,particularly an accelerated weathering test method in which a remoteplasma apparatus is used.

BACKGROUND ART

As for walls of residential houses and buildings and bodies ofautomobiles, coating films are often formed on their surfaces in orderto protect their appearances or provide glories. Such the coating filmsare degraded gradually due to the effects of sun light, water, changesin ambient temperature or the like during exposure to the outdoors forlong time and their appearances deteriorate.

The degradation of the coating film is generally evaluated as weatherresistance. This evaluation of the weather resistance is conducted byexposing the coating films in Okinawa in Japan or Florida in USA. Inthese areas, it is hot and wet and an amount of ultraviolet light ismuch, and the environment is harsh for coating films. Since suchexposure requires much time, various accelerated weathering testers havebeen developed as an apparatus capable of evaluating weather resistancein a short time.

However, in the previous accelerated weathering testers, some coatingfilms, which were considered to have adequate weather resistance by atest, actually caused problems such as cracks or discoloration with timeand its correlation with the results of actual exposure was notinsufficient. And, the test in which the conventional acceleratedweathering testers are used has an acceleration factor of about 10 to100 times, and an accelerated weathering tester, which can conduct thetest at higher acceleration factor, has been desired.

On the other hand, in a conventional accelerated weathering tester,loads applied to coating films for the accelerated degradation arelimited to factors such as ultraviolet light, water and changes inambient temperature, given from nature, and there were few attempts toapply another factors.

In Japanese Kokai Publication Hei-9-178727, there is disclosed a testmethod of organic materials, an accelerated degradation of coating filmsis conducted using a plasma generating apparatus of a type havingparallel plate type electrodes in this patent. However, there is noclear description on a correlation with the results of natural exposure.Further, in the case where a coating film is formed on a metal material,when plasma is irradiated directly to the coating film using such anapparatus, a metal portion must be masked because spark-discharge may begenerated to destroy the material, and in addition it is difficult tokeep a constant test conditions because the temperature of the coatingfilm is raised due to the occurrence of induction heating by ahigh-frequency. On the other hand, in the case where a coating film isformed on a porous inorganic material such as a ceramic board, there wasa problem that a volatile ingredient from the inorganic material had aneffect on test results in a high-vacuum condition in which plasma isirradiated.

When in order to resolve such the problems, the present inventorsstudied the results of natural exposure tests in detail, it wasrecognized that the degradation of coating films in natural exposureproceeded based on the degradation of the surface layer in the surfaceof a coating film. On the contrary, in the conventional acceleratedweathering tester, it became apparent that the degradation of a deeplayer simultaneously occurs. It is supposed that an adequate correlationwith the results of the natural exposure cannot be obtained due to suchthe different points.

If a usual plasma generating apparatus, which is described in JapaneseKokai Publication Hei-9-178727, is employed, it is impossible toselectively develop only the degradation of the surface layer and toresolve the problems described above.

SUMMARY OF THE INVENTION

In view of the above state of the art, it is an object of the firstpresent invention to provide an accelerated weathering test method,which gives the results having a high correlation with the results of anatural exposure and can significantly reduce a test duration.

In view of the above state of the art, it is another object of thesecond present invention to provide an accelerated weathering testmethod, which gives the results having a high correlation with theresults of a natural exposure by selectively developing degradation fromthe surface of a coating film.

The first present invention is an accelerated weathering test method ofaccelerating the degradation of the surface of an article to be treatedby irradiating plasma to said article to be treated,

wherein said plasma is generated by a remote plasma apparatus.

The above-mentioned article to be treated is preferably one having asurface on which a coating film is formed. In the present invention, theinterior of the above-mentioned remote plasma apparatus is preferablybrought into a reduced pressure. And, in the present invention, gas ispreferably introduced into the above-mentioned remote plasma apparatus.The above-mentioned gas is preferably an oxygen gas.

The second present invention is accelerated weathering test method ofaccelerating the degradation of the surface of an article to be treatedby irradiating an oxygen atom converted to a radical to said article tobe treated,

wherein said irradiation is conducted under the conditions of a degreeof vacuum of 0.4 to 10 torr and an oxygen flow rate of 50 to 500 ml/min.

The above-mentioned oxygen atom converted to a radical is preferablygenerated by a remote plasma apparatus using a power source of 20 to 200W. The above-mentioned accelerated weathering test method is preferablya method of developing selectively the degradation of the surface layerof the article to be treated. In the present invention, a filter isinstalled between a plasma generation section and a radical irradiationsection in order to selectively irradiate the oxygen atom converted to aradical from the remote plasma apparatus. The above-mentioned article tobe treated is preferably one having a surface on which a coating film isformed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view representing an example of a remote plasma apparatusused in the present invention.

FIG. 2 shows an electron microscope photograph of the surface of acoating film after a coating film degradation test by natural exposurewas conducted on a coating film of a sample used in Example during fiveyears.

FIG. 3 shows an electron microscope photograph of the surface of acoating film after a coating film degradation test with an acceleratedweathering tester of the metal halide lamp type, manufactured by DAIPLAWINTES CO., LTD. was conducted on a coating film of a sample used inExample.

FIG. 4 is a view showing a relationship between an amount of titaniumoxide in a coating film to be treated and color difference afterdegradation.

FIG. 5 is a view representing an example of a remote plasma apparatusused in the present invention.

FIG. 6 is a view showing the secular change of gloss retention (GR) inconducting an outdoor exposure test on samples A to C.

FIG. 7 is a view showing the secular change of color difference (ΔE) inconducting an outdoor exposure test on samples A to C.

FIG. 8 is a view showing the secular change of gloss retention (GR) inconducting an accelerated weathering test according to Example onsamples A to C.

FIG. 9 is a view showing the secular change of color difference (ΔE) inconducting an accelerated weathering test according to Example onsamples A to C.

FIG. 10 is a view showing the secular change of gloss retention (GR) inconducting an accelerated weathering test according to ComparativeExample 1 on samples A to C.

FIG. 11 is a view showing the secular change of color difference (ΔE) inconducting an accelerated weathering test according to ComparativeExample 1 on samples A to C.

FIG. 12 is a view showing the secular change of gloss retention (GR) inconducting an accelerated weathering test according to ComparativeExample 2 on samples A to C.

FIG. 13 is a view showing the secular change of color difference (ΔE) inconducting an accelerated weathering test according to ComparativeExample 2 on samples A to C.

FIG. 14 is a view showing the secular change of gloss retention (GR) inconducting an accelerated weathering test according to ComparativeExample 3 on samples A to C.

FIG. 15 is a view showing the secular change of color difference (ΔE) inconducting an accelerated weathering test according to ComparativeExample 3 on samples A to C.

FIG. 16 is a view showing a relationship between gloss retention (GR)and color difference (ΔE) in conducting an outdoor exposure test onsample A.

FIG. 17 is a view showing a relationship between gloss retention (GR)and color difference (ΔE) in conducting an outdoor exposure test onsample B.

FIG. 18 is a view showing a relationship between gloss retention (GR)and color difference (ΔE) in conducting an outdoor exposure test onsample C.

FIG. 19 is a view showing a relationship between gloss retention (GR)and color difference (ΔE) in conducting an accelerated weathering testaccording to Example on sample A.

FIG. 20 is a view showing a relationship between gloss retention (GR)and color difference (ΔE) in conducting an accelerated weathering testaccording to Example on sample B.

FIG. 21 is a view showing a relationship between gloss retention (GR)and color difference (ΔE) in conducting an accelerated weathering testaccording to Example on sample C.

FIG. 22 is a view showing a relationship between gloss retention (GR)and color difference (ΔE) in conducting an accelerated weathering testaccording to Comparative Example 1 on sample A.

FIG. 23 is a view showing a relationship between gloss retention (GR)and color difference (ΔE) in conducting an accelerated weathering testaccording to Comparative Example 1 on sample B.

FIG. 24 is a view showing a relationship between gloss retention (GR)and color difference (ΔE) in conducting an accelerated weathering testaccording to Comparative Example 1 on sample C.

FIG. 25 is a view showing a relationship between gloss retention (GR)and color difference (ΔE) in conducting an accelerated weathering testaccording to Comparative Example 2 on sample A.

FIG. 26 is a view showing a relationship between gloss retention (GR)and color difference (ΔE) in conducting an accelerated weathering testaccording to Comparative Example 2 on sample B.

FIG. 27 is a view showing a relationship between gloss retention (GR)and color difference (ΔE) in conducting an accelerated weathering testaccording to Comparative Example 2 on sample C.

FIG. 28 is a view showing a relationship between gloss retention (GR)and color difference (ΔE) in conducting an accelerated weathering testaccording to Comparative Example 3 on sample A.

FIG. 29 is a view showing a relationship between gloss retention (GR)and color difference (ΔE) in conducting an accelerated weathering testaccording to Comparative Example 3 on sample B.

FIG. 30 is a view showing a relationship between gloss retention (GR)and color difference (ΔE) in conducting an accelerated weathering testaccording to Comparative Example 3 on sample C.

FIG. 31 is a view showing a relationship between a degree of vacuum anda surface temperature rise at respective outputs.

FIG. 32 is a view representing a surface temperature rise at respectiveoutputs at an irradiation distance of 350 mm.

FIG. 33 is a view representing a surface temperature rise at respectiveoutputs at an irradiation distance of 150 mm.

FIG. 34 is a view representing the secular change of color difference atrespective outputs.

FIG. 35 is a view representing the secular change of color difference atrespective oxygen flow rates.

FIG. 36 is a view representing the secular change of color difference atrespective degrees of vacuum.

EXPLANATION OF THE NUMERICAL SYMBOLS

-   1 plasma generation section-   2 high-frequency power source-   3 sample stage-   4 vacuum pump-   5 flow of gas-   6 flow of neutral plasma-   7 plasma irradiation section-   8 remote plasma apparatus-   9 tube-   10 direction of current-   11 filter

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, the present invention will be described in detail.

A remote plasma apparatus used in the first present invention isprovided with a mechanism generating plasma persistently independent ofa sample stage on which an article to be treated is placed, and amechanism which can control a density of a neutral radical entering thearticle to be treated to any value by means of power applied to itselectrodes. While a plasma generation section and a plasma irradiationsection are located extremely close to each other in a usual plasmaapparatus, the plasma generation section and the plasma irradiationsection are located at a distance from each other in the above-mentionedremote plasma apparatus. Though its distance varies depending on anoutput of a power source to be used or required energy of plasma, when ahigh-frequency power source of, for example, about 200 W is used, it ispreferably several tens of cm and more preferably 20 to 60 cm. Since theplasma generation section and the plasma irradiation section are locatedat a distance from each other as mentioned above, an electron or an ionis deactivated before being irradiated and a neutral radical can beselectively irradiated to the article to be treated.

A power source in the above-mentioned plasma generating apparatus is notparticularly limited and for example, a high-frequency (generally, 13.56MHz) and a microwave (generally, 2450 MHz) can be employed. When plasmaby the above-mentioned high-frequency is used, an output thereof ispreferably 20 to 200 W.

FIG. 1 shows an example of the above-mentioned remote plasma apparatus.The remote plasma apparatus 8 includes the plasma generation section 1and the plasma irradiation section 7 located at a distance from eachother. This distance may be adjusted to 20 to 60 cm. In addition, thedistance between the plasma generation section 1 and the plasmairradiation section 7 described here refers to a distance between theplasma generation section 1 and a sample stage 3, which is movable upand down, installed in the plasma irradiation section 7. Ahigh-frequency power source 2 is connected to the plasma generationsection 1 as a power source, and therefore a density of a neutralradical entering the article to be treated can be controlled to anyvalue. And, a tube 9 for introducing gas is connected to the plasmageneration section 1. On the other hand, a vacuum pump 4 is connected tothe plasma irradiation section 7 and therefore an interior of the remoteplasma apparatus 8 can be brought into a reduced pressure.

An article to be treated in the accelerated weathering test method ofthe present invention, is not particularly limited, but usuallysubstances comprising organic materials, the surfaces of which aredegraded with time, are applied. As such the organic material, there aregiven various substrates such as metal materials, plastics, inorganicmaterials and woods having a coating film formed from a paint and acoating material on the surfaces thereof, in addition to substancescomposed of only an organic material such as plastic moldings or films.This coating film may be a free film. In the accelerated weathering testmethod of the present invention, since a remote plasma apparatus isused, there is no effect on a test resulting from the species of asubstrate on which a coating film is formed and the flexibility ofselecting the substrate is higher than a method described in JapaneseKokai Publication Hei-9-178727.

In the accelerated weathering test method of the present invention,first, an article to be treated, having a size adapted to theabove-mentioned plasma irradiation section of the remote plasmaapparatus, is placed on a sample stage as a sample. Then, the interiorof the apparatus is brought into a reduced pressure. Its degree ofvacuum is preferably adjusted so as to be about 0.1 torr to 5.0 torr.After making sure that the interior of the apparatus has been broughtinto a reduced pressure, treatment can be conducted by generatingplasma. By introducing gas into the apparatus in this step, radical canbe generated with efficiency. That is, in FIG. 1 previously described,after a vacuum pump 4 is started to bring the interior of the apparatus8 into a reduced pressure, gas is introduced in the direction of thearrow 5 through a tube 9, and finally neutral plasma is irradiated inthe direction of the arrow 6 to the sample on the sample stage 3.

As the gas of a radical source, there can be used, for example, oxygen,argon, helium and monomers having a double bond, but oxygen is desiredin consideration of bringing the gas into correspondence with adegradation factor in the natural exposure and an alteration of theradical after the plasma irradiation. The above-mentioned gas isintroduced into the apparatus, for example, at a flow rate of 100 to 300ml/min, and the degree of vacuum in the apparatus is preferably adjustedso as to be about 0.75 torr or lower.

In the accelerated weathering test method of the present invention, aplasma irradiation time, which will be a test time, can be arbitrarilyset. As a method of finding a time interval, which is proper as anirradiation time, there can be given, for example, a method ofconducting irradiation for a given length of time and finding a requiredirradiation time in view of the results of the test. And, as anothermethod, there may be employed a method in which a criterion is set forgloss retention and/or color difference of the coating film, and thegloss retention and/or color difference of a sample after a lapse of acertain test time is measured and the accelerated weathering test iscontinued until the measurements become below this criterion. In theaccelerated weathering test method of the present invention, since it ispossible to conduct a treatment in an extremely short time in comparisonwith a method using the conventional acceleration apparatus, theabove-mentioned test time may be appropriately selected so as to be, forexample, several hours or less in consideration of a sample.

A degree of degradation of the surface of the article to be treated,which has been treated by the accelerated weathering test method of thepresent invention, can be determined by visually evaluating anappearance and in addition to this, by measuring the gloss retention andthe color difference in the case where a coating film is formed on thesurface of the article to be treated.

The accelerated weathering test method of the present invention givesthe results having a higher correlation with the results of an actualexposure compared with a method using the conventional acceleratedweathering tester. This became apparent from measurements of secularchanges of the above-mentioned gloss retention and color difference ofthe coating film. That is, when the treatment for degradation accordingto the natural exposure and the accelerated weathering test method ofthe present invention was applied to two or more species of coatingfilms and the above-mentioned secular changes of the gloss retention andcolor difference was compared with one another, the correlations, whichhad not been found in the conventional accelerated weathering testmethod, were found.

On the other hand, the present inventors have newly found that the glossretention is in correlation with the color difference in the naturalexposure. And, this correlation was also identified in the acceleratedweathering test method of the present invention. On the contrary, in theconventional accelerated weathering tester, the correlation between thegloss retention and the color difference was not found, and thereforethis is considered to suggest, but not directly, that the acceleratedweathering test method of the present invention gives the results havinga higher correlation with the results of an actual exposure

As the reason for the above results, because it is supposed to occur adegradation reaction mainly based on a radical reaction, in the surfaceof a coating film, in the accelerated weathering test method using theremote plasma apparatus of the present invention, it is supposed thatlikewise in the natural exposure, a degradation reaction due to aradical reaction may take place predominantly.

And, in the remote plasma apparatus used in the present invention, thereis no fear of a temperature rise due to spark discharge or inductionheating by high-frequency even in the case where a coating film isformed on a metal material since the plasma generation section and theplasma irradiation section are located at a distance from each other.And, if a volatile ingredient is generated from a porous inorganicmaterial, there is little effect on the test results since particularlyactive ion species or electrons are not present in the plasmairradiation section.

Further, the above-mentioned remote plasma apparatus is also excellentin that it is possible to conduct a treatment in an extremely shorttime. The reason for this is assumed that while in a conventionalaccelerated tester utilizing a photochemical reaction, energy, which isgiven to the surface of an article to be treated, is about 1 eV, energyof active species in the above remote plasma apparatus is 10 to 100 eV.

An accelerated weathering test method of the second present invention isa method of developing selectively only degradation from the surfacelayer of the article to be treated by selectively irradiating theneutral oxygen radical to the surface of the article to be treated andcan perform stably an accelerated weathering test which gives theresults having a high correlation with the results of natural exposure.

The results of natural exposure tests of coating films and the testresults of coating films according to a conventional acceleratedweathering test method were investigated in detail, so that somedistinctive points became clear. One of them is that in the naturalexposure test, pigment particles were exposed to the surface (refer toFIG. 2). From this, it is thought that the degradation of a coating filmis predominantly caused by the degradation of the surface in which resinin the surface is lost by natural exposure test. On the other hand, in adegraded coating film treated according to tests using a conventionalaccelerated test apparatus, for example, a lamp type emphasizing a shortwavelength, pinholes having a diameter of 1 μm or less exist in thecoating film (refer to FIG. 3), and it is supposed that the degradationof a deep layer is simultaneously developed. It is thought that thenatural exposure test and the test using the conventional acceleratedtest apparatus are different in a mechanism of degradation from eachother like this and this point is considered as one of the causes of thefact that the results of the conventional accelerated weathering testdid not have an adequate correlation with the results of the naturalexposure.

The reason for the occurrence of such a difference is assumed that whenthe accelerated degradation is conducted using strong ultraviolet lightwith a short wavelength as with a test using the conventionalaccelerated degradation tester, a degradation factor cannot stay in thesurface of an article to be treated and the degradation is alsoaccelerated inside the article to be treated, but in a mild degradationcondition of nature, a degradation factor has an effect on only thesurface of the article to be treated and the degradation of the surfacelayer predominantly occurs.

As another one of such a different point between the natural exposuretest and the test using the conventional accelerated test apparatus,there can also be given a relationship between an amount of titaniumoxide in the coating film and color difference. As a result of measuringcolor difference in conducting the natural exposure tests on threespecies of coating films differing in an amount of titanium oxide,respectively, over 5 years, it was found that the color difference,namely, the degradation of coating film increased as the contenttitanium oxide in the coating film increased (refer to FIG. 4). It issupposed that this result reflects the fact that in the degradation ofthe coating film in the natural exposure, an effect of a photocatalystreaction by titanium oxide is large. That is, it is supposed that innatural conditions, titanium oxide in the vicinity of the surface layeris activated by ultraviolet light irradiated, and a photocatalystreaction occurs and thereby, the degradation of coating films mainlybased on the degradation of the surface occurs.

On the contrary, when light was irradiated to the same coating filmswith an accelerated weathering tester of the metal halide lamp type, anconventional accelerated weathering tester, the color differencedecreased as the content of titanium oxide increased, resulting in asmaller degradation of coating films (refer to FIG. 4). Such the testresults were opposed to that of the natural exposure test. The reasonwhy the opposed result was obtained is assumed that in the acceleratedweathering test using the accelerated weathering tester of the metalhalide lamp type, the irradiation of strong ultraviolet light causes notonly the degradation of the surface layer due to titanium oxide but alsothe degradation of the deep layer. That is, when an amount of titaniumoxide in the coating film is increased, masking capability of titaniumoxide significantly blocks the penetration of ultraviolet light into aninside of the coating films. Therefore, it is supposed that thedegradation of the deep layer is significantly blocked through blockingof ultraviolet light, and consequently the result that the coating filmbecomes resistant to the degradation as an amount of titanium oxideincreases is obtained. In the conventional accelerated weathering testercausing such a difference, it is difficult to predict adequately thedegradation of a coating film.

Based on the viewpoint described above, it was found that if it ispossible to conduct such an accelerated degradation test that thedegradation of the surface layer is predominant, it is possible toprovide an accelerated test method which gives the results having a highcorrelation with the results of natural exposure and can measure alifetime of the article to be treated more exactly. The presentinvention has been made based on such findings, and can repeat thedegradation in the surface of the coating film, which is similar to amechanism of the degradation from the surface (the degradation ofsurface layer) occurred in the natural exposure, using the remote plasmaapparatus by selectively irradiating the radical to the article to betreated under the specified conditions.

In the accelerated weathering test method of the present invention, thedegradation of the surface of the article to be treated is acceleratedby irradiating an oxygen atom converted to a radical to the article tobe treated. That is, when the accelerated degradation is conductedaccording to the method described in Japanese Kokai PublicationHei-9-178727, not only radical species but also electrons and ions areirradiated to the surface of the article to be treated and a thermalfactor is promoted to cause the surface temperature to increasesignificantly, and therefore such a method cannot give a sufficientcorrelation with the results of natural exposure. But, when theselective accelerated degradation is performed with radical species, thedegradation of surface layer is selectively developed, and therefore anaccelerated degradation test, the results of which have a highcorrelation with the results of natural exposure, can be conducted. And,since among radical species, the oxygen atom converted to a radical isrelatively stable, it is easy to handle and an accelerated degradationtest using it can be conducted efficiently.

In the present invention, it is necessary to limit the degree of vacuumand the oxygen flow rate in the irradiation within a proper range. Bylimiting these conditions, it is possible to develop the degradation ofthe surface with efficiency due to an oxygen atom converted to a radicaland an accelerated weathering test in an environment closer to naturalexposure can be conducted.

The above-mentioned degree of vacuum must be within a range of 0.4 torr(lower limit) to 10 torr (upper limit). The above degree of vacuumrefers to a degree of vacuum in a state of conducting the acceleratedweathering test of the present invention, namely, a degree of vacuum ina state in which plasma is generated using a power source of 20 to 200 Wand an oxygen gas is introduced into the interior of the remote plasmaapparatus at a flow rate of 50 to 500 ml/min. When the degree of vacuumis in a high vacuum of less than 0.4 torr, the degradation isaccelerated extremely fast since the oxygen atom converted to a radicalis stable, so that measurement error tends to occur and a goodaccelerated degradation of the coating film cannot be performed. When itis more than 10 torr, the control of conditions becomes difficult sincethe plasma becomes unstable. The above lower limit is more preferably0.6 torr, furthermore preferably 1.0 torr. The above upper limit is morepreferably 5 torr, furthermore preferably 2 torr.

As the gas of a radical source, an oxygen gas is used. Theabove-mentioned oxygen gas is introduced into the apparatus at a flowrate of 50 to 500 ml/min, and thereby, the degree of vacuum in theapparatus is preferably adjusted so as to be about 1.0 torr or lower.When the flow rate of the oxygen gas is less than 50 ml/min, an absoluteamount of oxygen molecules in plasma is small, and therefore a problemarises that oxygen molecules energized by electron are insufficient andconsequently an amount of neutral radical to be generated is reduced.When it is more than 500 ml/min, an exhaust amount of a vacuum pumpincreases and consequently a problem arises that a flow velocity ofoxygen gas increases and therefore an amount of radical reaching anarticle to be coated increases, so that the control of conditionsbecomes difficult.

In order to generate the above-mentioned oxygen atom converted to aradical with efficiency, a remote plasma apparatus may be used. As theabove remote plasma apparatus, there can be given an apparatus which isprovided with a mechanism generating plasma persistently independent ofa sample stage on which an article to be treated is placed, and amechanism which can control a density of a neutral radical entering thearticle to be treated to any value by means of power applied to itselectrodes.

A power source in the above plasma generating apparatus is notparticularly limited and for example, a high-frequency (generally, 13.56MHz) and a microwave (generally, 2450 MHz) can be employed. An output atthe above-mentioned power source is 20 to 200 W. When the output is lessthan 20 W, it becomes necessary to place the article to be treated closeto the plasma generating apparatus because of a low output and itbecomes difficult to selectively treat with only radical. And, when itis more than 200 W, ions or electrons also reach the article to becoated because of a too high output and the article to be coated isheated, and therefore it is impossible to conduct selective treatmentfrom the surface.

Further, when a temperature of the article to be coated is elevated, acorrelation with the results of the natural exposure becomes low since adegradation factor due to thermal degradation will have an effect.Particularly when a temperature of the article to be treated exceeds 50°C., reduction in the correlation is remarkable due to the fact that thiscondition significantly deviates from the actual natural phenomena(ambient temperature) and an effect of the thermal behavior of polymericresin becomes large, and therefore it is preferred to remain thetemperature of the article to be treated below 40° C. by establishingthe above-mentioned conditions.

FIG. 5 shows an example of a remote plasma apparatus which can be usedin the present invention. The remote plasma apparatus 8 includes theplasma generation section 1 and the plasma irradiation section 7 locatedat a distance from each other. This distance may be adjusted to 15 to 60cm. It is possible to selectively advance the degradation of the surfacelayer by adjusting this distance for an optimum in response to an outputof a power source. In addition, the irradiation distance described hererefers to a distance between the plasma generation section 1 and asample stage 3 to which a radical is irradiated. A high-frequency powersource 2 is connected to the plasma generation section 1 as a powersource, and therefore a density of a neutral radical entering thearticle to be treated can be controlled to any value. And, a tube 9 isconnected to the upper end of the plasma generation section 1. On theother hand, a vacuum pump 4 is connected to the sample stage 3 andtherefore an interior of the apparatus can be brought into a reducedpressure.

A filter 11 may be installed between the plasma generation section andthe radical irradiation section. The above-mentioned filter is aconductor having many holes provided along the direction of progress ofparticles. By trapping particles bearing electrical charges such aselectrons and ions with the conductor, only radical species selectivelypasses through the filter, and therefore only radical species convertedto a radical can be irradiated to the article to be treated. Bygrounding the filter, it is possible to release the charged electricityout of the apparatus.

An article to be treated in the accelerated weathering test method ofthe present invention, is not particularly limited, but usuallysubstances comprising organic materials, the surfaces of which aredegraded with time, are applied. As such the organic material, there aregiven various substrates such as metal materials, plastics, inorganicmaterials and woods having a coating film formed from a paint and acoating material on the surfaces thereof, in addition to substancescomposed of only an organic material such as plastic moldings or films.This coating film may be a free film. In the accelerated weathering testmethod of the present invention, since a remote plasma apparatus isused, there is no effect on a test resulting from the species of asubstrate on which a coating film is formed and the flexibility ofselecting the substrate is higher than a method described in JapaneseKokai Publication Hei-9-178727.

In the accelerated weathering test method of the present invention,first, an article to be treated, having a size adapted to theabove-mentioned radical irradiation section of the remote plasmaapparatus, is placed on a sample stage as a sample. Then, the interiorof the apparatus is brought into a reduced pressure. By introducing anoxygen gas into the apparatus at a flow rate of 50 to 500 ml/min aftermaking sure that the interior of the apparatus has been brought into areduced pressure and adjusting the degree of vacuum in the apparatus ina state of flowing the oxygen gas so as to be 0.4 torr to 10 torr, it ispossible to generate plasma with efficiency to conduct treatment. Thatis, in FIG. 4 previously described, after a vacuum pump 4 is started tobring the interior of the apparatus 8 into a reduced pressure, gas isintroduced in the direction of the arrow 5, and finally neutral plasmais irradiated in the direction of the arrow 6 to the sample on thesample stage 3.

In the accelerated weathering test method of the present invention, aradical irradiation time, which will be a test time, can be arbitrarilyset. However, since when the article to be treated is treated for anexcessively long time, it rises in temperature and factors of thermaldegradation have effects on the degradation of the article to betreated, it is preferred to treat it within a range that temperaturedifferentials of the article to be treated is 3° C. or less before andafter irradiation.

A degree of degradation of the surface of the article to be treated,which has been treated by the accelerated weathering test method of thepresent invention, can be determined by visually evaluating anappearance and in addition to this, by measuring the gloss retention andthe color difference in the case where a coating film is formed on thesurface of the article to be treated.

The accelerated weathering test method of the present invention givesthe results having a higher correlation with the results of an actualexposure compared with a method using the conventional acceleratedweathering tester. This became apparent from measurements of arelationship between an amount of titanium oxide and the degradation ofcoating films. That is, when the degradation of coating films accordingto the accelerated weathering test method of the present invention wasdeveloped on two or more species of coating films varying in an amountof titanium oxide, a result that the degradation of coating films isaccelerated as the amount of titanium oxide increases was obtained. Sucha result is similar to the degradation of coating films due to thenatural exposure.

As the reason why the above results were obtained, it is supposed thatin the natural exposure, the degradation reaction from the surface dueto a radical reaction predominantly takes place and supposed that in thepresent invention, since the oxygen atom converted to a radical isselectively irradiated, the degradation reaction from the surface due toa radical reaction predominantly takes place and therefore the resultsof the method of the present invention have a high correlation with theresults of natural exposure.

The accelerated weathering test method of the present invention definesspecified ranges of the output of the power source of the apparatus, thedegree of vacuum inside the apparatus and the oxygen rate introduced.Thereby, the rise in surface temperature of the article to be treated isinhibited, so that the effect on the degradation of a coating film canbe suppressed, and the amount of radical irradiation can be stabilized,so that the degradation from the surface of the article to be treatedcan be selectively developed in an accelerated weathering test.Accordingly, the accelerated weathering test method of the presentinvention is a test method which gives the results having a highcorrelation with the results of natural exposure.

BEST MODES FOR CARRYING OUT THE INVENTION

Hereinafter, the present invention will be described in more detail byway of examples, but the present invention is not limited to theseexamples.

INVENTION 1 Preparation of Sample

Each of aqueous acrylic emulsion coating compositions A, B and C havinga PWC of 22%, which contains titanium oxide and barium sulfate in theproportions shown in the following Table 1 and was toned in ivorysimilarly, was applied to a flat board cut in a predetermined size, onwhich an under layer comprising an impregnated sealer and a permeanceresistant sealer was formed, at a rate of 100 g/m² using a spray. Thiswas set for 5 minutes and then dried at 100° C. for 5 minutes to obtaina sample A, B or C, being an article to be treated, on the surface ofwhich a coating film is formed. TABLE 1 Coating compositions A B CTitanium oxide 3 8 15 Barium sulfate 15 10 3unit: PWC %

Outdoor Exposure Test

Weathering test by outdoor exposure test was conducted on theabove-mentioned samples A to C according to direct exposure tests (JIS Z2381 General requirements for outdoor exposure test, and JIS K 5600-7-6)at the Okinawa No.2 exposure field of Nippon Paint Co., Ltd. during fromSeptember 1994 to September 1999. The location of the exposure field isas follows.

Location: about 26° 20′ north latitude and about 1270 45′ minutes eastlongitude

Address: 373-309, Kadena-cho Aza Mizugama, Nakagami-gun, Okinawaprefecture

In the above-mentioned test, measurement of gloss retention and colordifference after lapses of one year, two years and five years wasconducted as follows.

Measurement of Gloss Retention and Color Difference

The gloss value of the samples was measured at 60° incidence-reflexangle using micro-TRI-gloss, which is a gloss meter manufactured byBYK-Gardner, before and after the test. The gloss retention (GR; GlossRetention) is obtained by multiplying the value obtained by dividing agloss value measured after the test by a gloss value measured before thetest by 100. On the other hand, the color difference (ΔE) was measuredwith a calorimeter CR-300 manufactured by KONICA MINOLTA HOLDINGS, INC.

EXAMPLE 1

A sample was placed on a sample stage 3 in a remote plasma apparatushaving a structure illustrated in FIG. 1, and an interior of theapparatus was brought into a reduced pressure of 0.5 torr by using avacuum pump 4. Then, an oxygen gas was continued to be flown at a flowrate of 200 ml/min in the direction of the arrow 5. In this state, adegree of vacuum was 0.75 torr. While keeping a temperature of thesample stage at 30° C., plasma was generated by a high-frequency powersource 2 using power of 50 W of high-frequency of 13.56 MHz andirradiated to the sample. The sample was taken out at time when 10minutes had elapsed since the initiation of irradiation and the glossretention (GR) and the color difference (ΔE) were measured. After themeasurement, the sample was replaced back into the remote plasmaapparatus, and plasma irradiation was repeated in a manner similar tothe case described above and the sample was measured. The totalirradiation time was 50 minutes. A temperature rise of the sample wasnot particularly recognized during the test and the acceleratedweathering test could be carried out without problems.

COMPARATIVE EXAMPLE 1 Accelerated Weathering Test Method With aConventional Apparatus No. 1

An accelerated weathering test was conducted on the above samples A to Creferring to JIS K5400 9.8 (Accelerated weathering) using Daipla MetalWeather (hereinafter, referred to as DMW), which is an acceleratedweathering tester of the metal halide lamp type, manufactured by DAIPLAWINTES CO., LTD. In the test, light irradiation of 4 hours was conductedusing a light source of 60 mW/cm² under the conditions of temperature of63° C. and humidity of 40%, and then after carrying out showering for 10seconds, the samples were held for 4 hours under the wet conditions oftemperature of 30° C. and humidity of 98%. This procedure was takes asone cycle and this cycle was repeated during a predetermined duration.In the test, the gloss retention (GR) and the color difference (ΔE) weremeasured after a lapse of specified time.

COMPARATIVE EXAMPLE 2 Accelerated Weathering Test Method With aConventional Apparatus No. 2

An accelerated weathering test was conducted on the above samples A to Creferring to JIS B 7753 (sunshine carbon-arc type weathering test) andJIS K 5400 9.8 (Accelerated weathering) using Sunshine Weather Meter(hereinafter, referred to as SWM), which is an accelerated weatheringtester of the sunshine carbon-arc type, manufactured by Suga TestInstruments Co., Ltd. In the test, light irradiation was conducted for aspecified duration using a light source of 2 mW/cm² under the conditionsof temperature of 63° C., humidity of 50% and continuous showering. Inthe test, the gloss retention (GR) and the color difference (ΔE) weremeasured after a lapse of specified time.

COMPARATIVE EXAMPLE 3 Accelerated Weathering Test Method With aConventional Apparatus No. 3

An accelerated weathering test was conducted on the above samples A to Creferring to JIS K5400 9.8 (Accelerated weathering) using Super UVTester (hereinafter, referred to as SUV), which is an acceleratedweathering tester of the metal halide lamp type, manufactured by IWASAKIELECTRIC Co., Ltd. In the test, light irradiation of 4 hours wasconducted using a light source of 100 mW/cm² under the conditions oftemperature of 63° C. and humidity of 40%, and then after carrying outshowering for 10 seconds, the samples were held for 4 hours under thewet conditions of temperature of 30° C. and humidity of 98%. Thisprocedure was takes as one cycle and this cycle was repeated during apredetermined duration. In the test, the gloss retention (GR) and thecolor difference (ΔE) were measured after a lapse of specified time.

Secular Change of Gloss Retention and Color Difference

The respective graphs showing the secular change of the gloss retention(GR) and the color difference (ΔE) obtained by the above respectivetests were shown in FIGS. 6 and 7 (Outdoor exposure tests), FIGS. 8 and9 (Examples) and FIGS. 10 and 11 (Comparative Example 1), FIGS. 12 and13 (Comparative Example 2), and FIGS. 14 and 15 (Comparative Example 3).

Viewing these graphs, it is verified that while the results of Example 1of the present invention resemble Outdoor exposure tests in patterns ofchanges in the gloss retention and the color difference, the results ofComparative Example 1 are different in patterns of change in the glossretention and the results of Comparative Example 2 are different inpatterns of change in the color difference from Outdoor exposure tests,respectively.

Endurance Time

In the accelerated weathering test method, the instant when the glossretention declined to 50% was considered to be as the instant when thecoating film had been degraded, and the test time that elapses beforethe gloss retention declined to 50% was defined as an endurance time,the values were read out from FIGS. 6, 8, 10, 12 and 14. The results areshown in Table 2. TABLE 2 Outdoor Compara- Compara- Exposure tive tiveTest Example Example 1 Example 2 Comparative (unit: (unit: (unit: (unit:Example 3 year) minute) hour) hour) (unit: hour) Sample A 2.2 38 1003100 310 Sample B 1.3 37 110 2200 450 Sample C 1.0 33 90 3200 620

From Table 2, it is evident that the accelerated weathering test ofExamples can reach the endurance time in shorter time than theaccelerated weathering test of Comparative Examples 1 to 3 and cansignificantly reduce the time required for the tests.

And, in the outdoor exposure tests, decreasing order of the endurancetime of respective samples is A, B, C. Since this result agrees withincreasing order of an amount of titanium oxide, this result isconsidered to suggest that the degradation proceeds due to aphotocatalyst reaction of titanium oxide in the surface of a coatingfilm. The order of length of the above endurance time in the acceleratedweathering tests of Examples is the same as outdoor exposure tests andit is thought that a degradation reaction similar to outdoor exposuretests occurs. On the contrary, in the accelerated weathering test ofComparative Examples, the above-mentioned relationship does not hold forany case, and there is a high probability that a different reactionoccurs. From these results, it can be said that the acceleratedweathering test method of the present invention gives the results havinga higher correlation with the results of an outdoor exposure than theaccelerated weathering test methods of Comparative Examples.

Color Difference at a Maximum Endurance Time

In the above outdoor exposure tests and the accelerated weatheringtests, the endurance time of sample (for example, sample A in the caseof outdoor exposure tests and Examples), of which the above endurancetime is maximum, is defined as a maximum endurance time T_(L) (forexample, 2.2 years in the case of outdoor exposure tests), and thevalues of color difference ΔE_(L) of samples A to C at the above T_(L)were read out from Figures. The results are shown in Table 3. TABLE 3Outdoor Compara- Compara- Exposure Comparative tive tive Test ExampleExample 1 Example 2 Example 3 Sample A 1.5 1.4 0.7 0.8 0.6 Sample B 2.91.8 0.7 0.7 0.3 Sample C 4.5 2.6 0.4 0.8 0.3

In Outdoor exposure tests, the above ΔE_(L) is an indicator representingthe degradation state of a coating film and ΔE_(L) takes smaller valueas the weather resistance of a coating film becomes large. Therefore,the order of the weather resistance of three species of coating films isA, B, C in decreasing order from the results of Outdoor exposure tests.Only the results of the accelerated weathering tests of Examples exhibitthe same order as the result of Outdoor exposure tests. The order of thevalues of the above ΔE_(L) in Comparative Examples is absolutelydifferent from the result of Outdoor exposure tests. Accordingly,outdoor exposure test, namely, the weather resistance of an actualcoating film cannot be predicted from the values of the ΔE_(L) inComparative Examples, and on the contrary the weather resistance of anactual coating film can be predicted from the values of the ΔE_(L) inExamples.

Relationship Between the Gloss Retention and the Color Difference

The present inventors have found that the relationships between thegloss retention and the color difference in the outdoor exposure testexhibit a linear correlation as shown in FIGS. 16 to 18. The correlationbetween the gloss retention and the color difference was also recognizedin the results in Examples shown in FIGS. 19 to 21. The correlations inthe outdoor exposure test were shown in Table 4 and the correlations inExample were shown in Table 5. TABLE 4 Approximate Coefficient ofcorrelation Sample expression (R²) Sample A ΔE = −0.068GR + 4.97 0.844Sample B ΔE = −0.081GR + 5.61 0.829 Sample C ΔE = −0.115GR + 7.31 0.876

TABLE 5 Approximate Coefficient of correlation Sample expression (R²)Sample A ΔE = −0.027GR + 2.80 0.981 Sample B ΔE = −0.037GR + 3.85 0.958Sample C ΔE = −0.047GR + 4.58 0.964

On the other hand, as shown in FIGS. 22 to 30, respectively, theabove-mentioned correlation was not recognized in Comparative Examplesaccording to the conventional accelerated weathering test.

INVENTION 2 Preparation of Sample

Each of aqueous acrylic emulsion coating compositions A, B and C, whichcontains titanium oxide and barium sulfate in the proportions to be 23%as the total PWC and was toned in ivory similarly, was applied to a flatboard cut in a predetermined size, on which an under layer comprising animpregnated sealer and a permeance resistant sealer was formed, at arate of 100 g/m² using a spray. This was set for 5 minutes and thendried at 100° C. for 5 minutes to obtain a sample A, B or C, being anarticle to be treated, on the surface of which a coating film is formed

Outdoor Exposure Test

Weathering test by outdoor exposure test was conducted on theabove-mentioned samples according to direct exposure tests (JIS Z 2381General requirements for outdoor exposure test, and JIS K 5600-7-6) atthe Okinawa No.2 exposure field of Nippon Paint Co., Ltd. during fromSeptember 1994 to September 1999. The location of the exposure field isas follows.

Location: about 26° 20′ north latitude and about 127° 45′ minutes eastlongitude

Address: 373-309, Kadena-cho Aza Mizugama, Nakagami-gun, Okinawaprefecture

In the above-mentioned test, the surface after a lapse of five years wasphotographed with an electron microscope. The result was shown in FIG.2. From this picture, it is obvious that the degradation of the surfacelayer occurs.

Accelerated Weathering Test Method with a Conventional Apparatus

An accelerated weathering test was conducted on the above samples A to Creferring to JIS K5400 9.8 (Accelerated weathering) using Daipla MetalWeather (hereinafter, referred to as DMW), which is an acceleratedweathering tester of the metal halide lamp type, manufactured by DAIPLAWINTES CO., LTD. In the test, light irradiation of 4 hours was conductedusing a light source of 60 mW/cm² under the conditions of temperature of63° C. and humidity of 40%, and then after carrying out showering for 10seconds, the samples were held for 4 hours under the wet conditions oftemperature of 30° C. and humidity of 98%. This procedure was takes asone cycle and this cycle was repeated during a predetermined duration.The surface of the coating film after the irradiation of 256 hours wasphotographed with an electron microscope. The result was shown in FIG.2. From FIG. 3, it is obvious that not only the degradation of thesurface layer but also the degradation of the deep layer occur in theaccelerated degradation test method with the conventional apparatus.

Accelerated Weathering Test Method by Irradiating an Oxygen AtomConverted to a Radical to an Article to be Treated

A sample was placed on a sample stage 3 in a remote plasma apparatushaving a structure illustrated in FIG. 5, and an interior of theapparatus was brought into a reduced pressure by using a vacuum pump 4.Then, an oxygen gas was continued to be flown at a constant flow rate inthe direction of the arrow 5. Plasma was generated by using ahigh-frequency power source 2 (13.56 MHz) and the generated oxygen atomconverted to a radical was irradiated to the sample.

EXAMPLE 2 AND COMPARATIVE EXAMPLE

In the apparatus, there were measured temperature rises (° C.) ofsamples in setting a high-frequency power of a high-frequency powersource 2 (13.56 MHz) at 25 W, 50 W, 100 W and 300 W and a degree ofvacuum at 0.4 torr, 0.6 torr, 0.8 torr and 1.0 torr taking an oxygenflow rate as 350 ml/min, a distance between a plasma generation section1 and a sample stage 3 as 150 mm and an irradiation time as 60 minutes.The results were shown in FIG. 31.

It was found from FIG. 31 that in the case where the degree of vacuumwas 0.4 torr, the temperature rises of some samples were found. In thecase where the high-frequency power was 300 W, the temperature rises ofthe samples were noticeable even though the degree of vacuum were 0.8torr and 1.0 torr.

Surface Temperature Rise at Respective Outputs at an IrradiationDistance of 350 mm

In the apparatus, there were measured temperature rises (° C.) ofsamples in setting a high-frequency power of a high-frequency powersource 2 (13.56 MHz) at 50 W, 100 W and 300 W taking an oxygen flow rateas 350 ml/min, a degree of vacuum as 1.0 torr and a distance between aplasma generation section 1 and a sample stage 3 as 350 mm.Relationships between the irradiation time of radical and thetemperature rise were shown in FIG. 32.

FIG. 32 showed that in the case where the high-frequency power was 100 Wor 300 W, the temperature rises of the samples were noticeable becauseof the high output of the high-frequency power even though theirradiation distance was set at 350 mm.

Surface Temperature Rise at Respective Outputs at an IrradiationDistance of 150 mm

In the apparatus, there were measured temperature rises (° C.) ofsamples in setting a high-frequency power of a high-frequency powersource 2 (13.56 MHz) at 50 W, 100 W, 300 W and 600 W taking an oxygenflow rate as 350 ml/min, a degree of vacuum as 1.0 torr and a distancebetween a plasma generation section 1 and a sample stage 3 as 150 mm.Relationships between the irradiation time of radical and thetemperature rise were shown in FIG. 33.

FIG. 33 showed that in the case where the high-frequency power was 300 Wor 600 W, the temperature rise of the sample was noticeable. Therefore,the degradation is developed and it is impossible to selectively developonly the degradation of the surface layer.

Color Difference at Respective Outputs at an Irradiation Distance of 150mm

In the remote plasma apparatus illustrated in FIG. 5, there was measuredthe secular change of color difference in setting a high-frequency powerof a high-frequency power source 2 (13.56 MHz) at 15 W, 50 W and 300 Wtaking an oxygen flow rate as 350 ml/min, a degree of vacuum as 1.0 torrand a distance between a plasma generation section 1 and a sample stage3 as 150 mm. Relationships between the irradiation time of radical andthe color difference are shown in FIG. 34. In addition, the colordifference was measured with a calorimeter CR-300 manufactured by KONICAMINOLTA HOLDINGS, INC.

It was found from FIG. 34 that in the case where the output of ahigh-frequency power source is 300 W, since the color differenceincreases rapidly even though the irradiation time is short, ameasurement error tends to be large, and therefore it becomes difficultto predict the degradation state of the coating film exactly. And, thecolor difference hardly changes and an effect of accelerated degradationis very poor in the case where the output of a high-frequency powersource is 15 W.

Change in Color Difference Based on the Difference in an Oxygen FlowRate

In the remote plasma apparatus illustrated in FIG. 5, there was measuredthe secular change of color difference in setting an oxygen flow rate at30 ml/min, 350 ml/min and 600 ml/min taking a degree of vacuum as 1.0torr, a distance between a plasma generation section 1 and a samplestage 3 as 150 mm and an output of a high-frequency power source (13.56MHz) as 50 W. Relationships between the irradiation time of radical andthe color difference are shown in FIG. 35.

It was found from FIG. 35 that in the case where the oxygen flow rate is600 ml/min, since the color difference increases rapidly even though theirradiation time is short, a measurement error tends to be large, andtherefore it becomes difficult to predict the degradation state of thecoating film exactly. And, a speed of the accelerated degradation isslow in the case where the oxygen flow rate is 30 ml/min.

Change in Color Difference Based on the Difference in a Degree of Vacuum

In the remote plasma apparatus illustrated in FIG. 5, there was measuredthe secular change of color difference in setting a degree of vacuum at0.3 torr, 1.0 torr and 12.0 torr taking an oxygen flow rate as 350ml/min, a distance between a plasma generation section 1 and a samplestage 3 as 150 mm and an output of a high-frequency power source (13.56MHz) as 50 W. Relationships between the irradiation time of radical andthe color difference are shown in FIG. 36.

It was found from FIG. 36 that in the case where the degree of vacuum is0.3 torr, since the color difference increases rapidly even though theirradiation time is short, a measurement error tends to be large, andtherefore it becomes difficult to predict the degradation state of thecoating film exactly. And, a speed of the accelerated degradation isslow in the case where the degree of vacuum is 12.0 torr.

Change in Color Difference Based on the Difference in an Amount ofTitanium Oxide

On the three species of coating films, in which the contents of titaniumoxide are 16.7 weight %, 44.4 weight % and 72.2 weight %, respectively,the outdoor exposure test was conducted at the conditions describedabove for 5 years in Okinawa, and the above-mentioned oxygen radicalirradiation of 50 minutes, was conducted with a distance between aplasma generation section and a sample stage being 150 mm under theconditions of an oxygen flow rate of 400 ml/min and a degree of vacuumof 1.2 torr using the above-mentioned remote plasma apparatus and thehigh-frequency power source (13.56 MHz) of 50 W. And, as theconventional accelerated weathering test method, an acceleratedweathering test was conducted on the above samples referring to JIS K5400 9.8 (Accelerated weathering) using Super UV Tester (hereinafter,referred to as SUV), which is an accelerated weathering tester of themetal halide lamp type, manufactured by IWASAKI ELECTRIC Co., Ltd. Inthe test, light irradiation of 4 hours was conducted using a lightsource of 100 mW/cm² under the conditions of temperature of 63° C. andhumidity of 40%, and then after carrying out showering for 10 seconds,the samples were held for 4 hours under the wet conditions oftemperature of 30° C. and humidity of 98%. This procedure was takes asone cycle and this cycle was repeated during 1200 hours. Each colordifference of degraded coating films was measured. The results ofmeasurement are shown in FIG. 4.

As is apparent from FIG. 4, the test results obtained by the acceleratedweathering test method of the present invention shows that the colordifference increases as the titanium oxide content increases as with thetest results obtained by the natural exposure, but the acceleratedweathering test with SUV shows the adverse results. From this result, itbecomes apparent that the accelerated weathering test method of thepresent invention gives the results having a high correlation with theresults of natural exposure.

INDUSTRIAL APPLICABILITY

In accordance with the present invention, it is possible to provide theaccelerated weathering test method, which gives the results having ahigh correlation with the results of natural exposure and cansignificantly reduce a test duration.

By the way, this application is a patent application concerning theresults of researches commissioned from the nation [commissionedresearch concerning “Development in resources recycling type coatingcomposition having a high durability and coating system for technicaldevelopment of next generation housing (limited to concerning resourcesrecycling type housing technical development)” of Ministry of Economy,Trade and Industry, subject to applications of Article 30 of Specialmeasures law on Industrial vitality reproduction].

1. An accelerated weathering test method of accelerating the degradationof the surface of an article to be treated by irradiating plasma to saidarticle to be treated, wherein said plasma is generated by a remoteplasma apparatus.
 2. The accelerated weathering test method according toclaim 1, wherein the article to be treated is one having a surface onwhich a coating film is formed.
 3. The accelerated weathering testmethod according to claim 1, wherein the interior of the remote plasmaapparatus is brought into a reduced pressure.
 4. The acceleratedweathering test method according to claim 1, wherein gas is introducedinto the remote plasma apparatus.
 5. The accelerated weathering testmethod according to claim 4, wherein the gas is an oxygen gas.
 6. Anaccelerated weathering test method of accelerating the degradation ofthe surface of an article to be treated by irradiating an oxygen atomconverted to a radical to said article to be treated, wherein saidirradiation is conducted under the conditions of a degree of vacuum of0.4 to 10 torr and an oxygen flow rate of 50 to 500 ml/min.
 7. Theaccelerated weathering test method according to claim 6, wherein theoxygen atom converted to a radical is generated by a remote plasmaapparatus using a power source of 20 to 200 W.
 8. The acceleratedweathering test method according to claim 6, wherein the acceleratedweathering test method is a method of developing selectively thedegradation of the surface layer of the article to be treated.
 9. Theaccelerated weathering test method according to claim 7, wherein afilter is installed between a plasma generation section and a radicalirradiation section in order to selectively irradiate the oxygen atomconverted to a radical from the remote plasma apparatus.
 10. Theaccelerated weathering test method according to claim 6, wherein thearticle to be treated is one having a surface on which a coating film isformed.
 11. The accelerated weathering test method according to claim 2,wherein gas is introduced into the remote plasma apparatus.
 12. Theaccelerated weathering test method according to claim 3, wherein gas isintroduced into the remote plasma apparatus.
 13. The acceleratedweathering test method according to claim 7, wherein the acceleratedweathering test method is a method of developing selectively thedegradation of the surface layer of the article to be treated.
 14. Theaccelerated weathering test method according to claim 8, wherein afilter is installed between a plasma generation section and a radicalirradiation section in order to selectively irradiate the oxygen atomconverted to a radical from the remote plasma apparatus.
 15. Theaccelerated weathering test method according to any one of claim 7,wherein the article to be treated is one having a surface on which acoating film is formed.
 16. The accelerated weathering test methodaccording to claim 8, wherein the article to be treated is one having asurface on which a coating film is formed.
 17. The acceleratedweathering test method according to claim 9, wherein the article to betreated is one having a surface on which a coating film is formed.